This invention relates to calixarenes, and more particularly to certain novel calixarenes, to a method of rendering substrate surfaces water repellent using calixarenes, and to substrates having water repellent surfaces produced thereby.
Calixarenes are amphiphilic molecules whose general structures is that of a molecular bowl on legs with the rim of the bowl lined by hydroxyl groups and the legs consisting of long chain alkyl groups. A detailed review of the different types of calixarenes and their methods of manufacture is given in Bohmer, Angew. Chem. Int. Ed. Engl. 1995, 34, 713-745, the entire disclosure of which is incorporated herein by reference for all purposes.
It has now been found that the hydroxyl groups lining the rim of the bowl of calixarenes can bond strongly to hydrophilic substrates and that if the calixarene also has hydrophobic pendant legs this can impart a highly water repellent surface to the substrate.
According to a first aspect of the invention, therefore, there is provided a method of imparting a water repellant surface to a hydrophilic substrate which comprises contacting the substrate with a solution or dispersion of a suitable calixarene in a liquid medium.
There are three main types of calixarene, prepared respectively from phenols, from resorcinols and from pyrogallols and aldehydes. Whilst the method of the invention is generally applicable to calixarenes, it is especially concerned with calixarenes derived from resorcinol, which in this specification will henceforth be termed xe2x80x9cresorcarenesxe2x80x9d.
In another aspect, the present invention provides a new class of resorcarenes having the general structure I below: 
wherein X is hydrogen, a C1 to C4 alkyl group, a substituted or unsubstituted amino group, or aminoalkyl group;
Y is OH or OCH2COORxe2x80x2, where Rxe2x80x2 is a C1 to C4 alkyl group;
R is a C1 to C18 fluoro-substituted alkyl group, and
n is 1 or 3, and
wherein each X, Y, Rxe2x80x2 and R group can be the same or different.
The method of the invention can be applied to a wide range of hydrophilic substrates including, for example, paper, cotton, wood, leather, stone, glass, hydrophilic synthetic fabrics, and hydrophilic polymeric materials.
Any suitable calixarene can be used in the method of the invention, provided that it has pendant legs imparting the desired water repellent properties to the substrate.
The pendant legs are preferably long chain hydrocarbon or fluorocarbon groups, having preferably from 5 to 15 carbon atoms in the chain, or long chain polyether groups. Long chain fluorocarbon groups are particularly preferred since these can impart both waterproofing and oil-proofing properties to a surface. The pendant legs preferably comprise long chain alkyl or fluoroalkyl groups, which terms, in this specification, include saturated and unsaturated (alkene and alkyne) groups, and which may also comprise other substituents.
Resorcarenes are particularly preferred for use in the method of the present invention, since it has been found that the water repellent properties imparted by these compounds are particularly persistent, and are not easily destroyed, for example, by washing. The resorcarenes are also particularly effective in imparting water repellency to rough surfaces. The most preferred resorcarenes for use in the method of the present invention are the new fluoro-substituted resorcarenes described hitherto.
Without intending the invention to be bound by any particular theory, it is believed that the improved water repellent properties obtained using calixarenes may be due to their ability to form multilayers in thin fibres. This property is described in relation to resorcarenes by Davis and Sterling in J. Am. Chem. Soc. 1995, 117, 10385-10386.
Certain preferred resorcarenes for use in the present invention have pendent legs comprising unsaturated hydrocarbon chains. Some of these compounds are new and accordingly comprise a further aspect of the invention. The presence of double bonds in the unsaturated chains provides the possibility for cross-linking reactions to be initiated, which could, for example, improve the binding of the resorcarene to the substrate surface, or improve the strength of the film (multilayer) if present, or provide sites for binding other reactive groups onto the resorcarene. Cross linking can be accomplished, for example, by the use of ultraviolet light, or by other free radical generating cross linking methods.
Preferably the resorcarene is one in which X is hydrogen. Other preferred resorcarenes for use in the present invention are those in which:
In the method of the invention, the calixarene solution or dispersion can simply be sprayed onto the substrate, or the substrate can be dipped into the solution or dispersion as appropriate. The calixarene is preferably applied dissolved or dispersed in a hydrophobic organic solvent, for example, hexane, dichloromethane or toluene.
The new resorcarenes having fluorinated pendant legs are preferably applied in solution or dispersion in an acetone/ethanol mixture.
The method can be carried out at any suitable temperature, although ambient temperatures are usually sufficient and heating is not normally necessary.
The concentration of the calixarene in solution can be, for example, from 0.001 to 10% by weight, but is preferably from 0.01 to 5% and more preferably around 0.1 to 1% by weight, based on the weight of the solution.
The invention is illustrated by the following Examples: